How to remove easily the white areas which appears during texturing a surface with uv maps
Those white faces appear because they are not linked to the same texture as the rest of the model. This can happen if you for example add new faces after the rest of the model has been linked to the texture. Fixing: 


Make sure the faces which are visible as white are actually unwrapped
Hit A to select all faces
In UV / Image Editor hit A to select all faces
In the bottom of the UV / Image Editor click the Select image icon next to either new/open buttons or the texture name, and select the image you want to use. (even if the field shows the image already, it might not be applied to all faces)